This invention relates to a process for the preparation of 1,2-fused five-membered or six-membered 1,3-dinitrogen-heterocyclic compounds and their use as anti-corrosion agents. The compounds, some of which are known, have the general formula ##STR4## wherein A denotes an optionally substituted, optionally polynuclear ortho- or peri-arylene radical and B denotes an optionally substituted alkylene chain ##STR5## IN WHICH R.sup.1 and R.sup.2 individually represent hydrogen and/or optionally substituted aliphatic, cycloaliphatic, araliphatic or aromatic radicals and
n represents an integer from 3 to 6, especially 3 to 5, PA1 B denotes an optionally substituted 1,8-naphthylene, 2,2'-diphenylene or 4,5-phenanthrylene radical. Some compounds of this nature have already been disclosed. In particular, these are compounds of the formula I, in which PA1 B denotes an aliphatic hydrocarbon chain --(CH.sub.2).sub.n --. PA1 B denotes an optionally substituted alkylene chain ##STR7## in which R.sup.1 and R.sup.2 in particular represent hydrogen and/or optionally substituted aliphatic, cycloaliphatic, araliphatic or aromatic radicals and PA1 n represents a number from 3 to 6, especially 3 to 5, PA1 B denotes an optionally substituted 1,8-naphthylene, 2,2'-diphenylene or 4,5-phenanthrylene radical,
Or
It is known to prepare these compounds by starting from o-nitrochlorobenzenes and alkyleneimines, which are condensed to N-[o-nitrophenyl]-alkyleneimines. These are converted to the 1,2-alkylenebenzimidazoles: [J. Chem. Soc. 3275 (1955); J. Chem. Soc. 1666-1669 (1963)] either directly by reduction with TiCl.sub.3 in concentrated hydrochloric acid [Tetrahedron (London) 24 (1968) 12, 4581-8] or by catalytic reduction followed by oxidation with Caro's acid [Ber. 41, 682 (1908)] or with peroxytrifluoroacetic acid [J. Am. Chem. Soc. 83, 3518 (1961)] or by diazotisation and thermal decomposition of the axide, obtainable by a Sandmeyer reaction, in nitrobenzene at 170.degree. C. Furthermore, 1,2-tetramethylenebenzimidazole has been obtained in only 16% yield by condensation of nitrobenzene with N-lithium-piperidine [Ann. 594, 159 (1955)]. Finally, some 1,2-alkylenebenzimidazoles have been prepared by cyclising condensation of o-phenylenediamine with .omega.-halogenocarboxylic acid iminoether hydrochlorides [J. Org. Chem. 27, 2165 (1962)].
However, probably none of these proposed methods deserves consideration as the basis of an industrially economical process, since on the one hand they comprise expensive process steps and on the other they only give low yields.